package com.hspedu.newData.dmsxl.树.二叉树的遍历.迭代;

import com.hspedu.newData.dmsxl.ds.TreeNode;
import org.junit.Test;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

/**
 * @Author: yh
 * @description: 
 * @CreateTime: 2025-04-23 
 * @Version: 1.0
 */

public class LC144二叉树的前序遍历 {


    // 递归遍历
    public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        if (root == null) return list;

        Stack<TreeNode> stack = new Stack<>();

        stack.push(root);

        while (!stack.isEmpty()){
            TreeNode node = stack.pop();
            list.add(node.val);

            if (node.right != null){
                stack.push(node.right);
            }
            if (node.left != null){
                stack.push(node.left);
            }
        }

        return list;
    }

    @Test
    public void test() {
        // 测试代码

        TreeNode t7 = new TreeNode(7);
        TreeNode t6 = new TreeNode(6);
        TreeNode t5 = new TreeNode(5);
        TreeNode t4 = new TreeNode(4);
        TreeNode t3 = new TreeNode(3,t6,t7);
        TreeNode t2 = new TreeNode(2,t4,t5);
        TreeNode t1 = new TreeNode(1,t2,t3);

        preorderTraversal(t1);
        System.out.println("==========");

    }
}
